A major concern with the utilization of certain fuels in directly fired conventional power generation systems and other processes is the particulates produced by combustion of the fuels. These particulates remain in the combustion gas stream. Because the gas stream running such systems can adversely impact on the life of the equipment, the gas stream should be substantially free of the particulate matter. Although conventional particulate removal devices may be used to remove some of the larger solid particulate matter from combustion gas streams, these devices generally fail to remove the smaller particulates from the streams. Similar problems also exist in many gas streams in which the particulate suspended matter originates from other than combustion.
U.S. Pat. No. 5,353,721 to Mansour, et al. and U.S. Pat. No. 5,197,399 to Mansour, et al., which are incorporated herein in their entirety by reference thereto for all purposes, describe a pulsed combustion apparatus and process for acoustically agglomerating particulates produced by the combustion of fuels so that the particulates may be removed from the combustion effluent stream. Once the particles are removed from the combustion effluent stream, the stream can then be used in various processes and systems. For example, in one embodiment, the effluent stream can be used to rotate a turbine for producing electricity.
Tests conducted in this mode in a process development unit (PDU) with pulverized bituminous coal and four different sorbents for sulfur capture provided the following results: (1) the combustion efficiency exceeded 99 percent; (2) sulfur capture was as high as 98 percent; (3) NOx emissions were in the range of 0.3 to 0.6 lb/MMBtu; and (4) the solids loading in cyclone exit flue gas (analogous to turbine inlet solids loading) was as low as 23 ppmw. The solids loading result greatly surpassed the original target goal of 100 to 150 ppmw and was good enough to meet the New Source Performance Standards (NSPS) for particulate emissions from power plants (<0.03 lb/MMBtu).
However, while the operation in the combustion or fuel lean mode provided satisfactory and encouraging results, the process was constrained thermodynamically and presented various problems related to emissions control. Specifically, the following limitations became apparent:                Sulfur retention or calcium utilization decreases with an increase in operating temperature under oxidizing or fuel lean conditions. For example, the Ca/S molar feed ratio required for 95% sulfur capture is very favorable at temperatures up to about 1,000° C. (1,832° F.) but rises sharply with further increase in temperature. This constrains the gas turbine inlet temperature and in turn the cycle or plant efficiency.        Although pulse combustors are inherently low NOx devices, oxidizing mode of operation, presence of fuel bound nitrogen and high temperature all favor NOx formation. Therefore, further NOx reduction, especially in the context of rising gas turbine inlet temperature requirement, was needed.        Higher temperatures (>1,000° C. or 1,832° F.) in the agglomeration chamber favor acoustic agglomeration, but not sulfur capture. This tends to limit the extent of decrease in the solids loading in cyclone exit flue gas.        
As such, a need currently exists for an improved agglomeration apparatus and process.